1. Field of the Invention
This invention relates generally and specifically to secure playback of digital audio, video or other content from memory cards, compacts disks or other media.
2. Related Art
The potential of electronic distribution of copyrighted music over the Internet, by other communication systems or through retail kiosks, is being limited by concerns about unauthorized copying of the music. This is also the case for other audio, as well as video, content. The content is typically provided to the ultimate customer in encrypted form, and the customer records the encrypted content files onto some storage media, such as a personal computer memory, a memory of a portable playing device, a writable compact disk (CD) or a non-volatile memory card. Providers of the content would like to eliminate the possibility of unauthorized copying of the content but have to be satisfied with taking steps that minimize the amount of copying that occurs. This includes providing protection of the content on the recording media. The protection of content stored on non-volatile memory cards is described herein, as specific examples, but the same content protection techniques can be applied to compact disks or other recordable media.
There are several commercially available non-volatile memory cards that are suitable for use as the content data storage media. One is the CompactFlash (CF) card, another is the MultiMediaCard (MMC), and yet another is the Secure Digital (SD) memory card that is closely related to the MMC card. All three, and others, are available in various storage capacities from SanDisk Corporation of Sunnyvale, Calif., assignee of the present application. The physical and electrical specifications for the MMC are given in “The MultiMediaCard System Specification” that is updated and published from time-to-time by the MultiMediaCard Association (“MMCA”) of Cupertino, Calif. Versions 2.11 and 2.2 of that Specification, dated June 1999 and January 2000, respectively, are expressly incorporated herein by this reference. The MMC products are also described in a “MultiMediaCard Product Manual,” Revision 2, dated April 2000, published by SanDisk corporation, which Manual is expressly incorporated herein by this reference. Certain aspects of the electrical operation of the MMC products are also described in co-pending patent applications of Thomas N. Toombs and Micky Holtzman, Ser. Nos. 09/185,649 and 09/186,064, both filed Nov. 4, 1998, and assigned to SanDisk Corporation. The physical card structure and a method of manufacturing it are described in U.S. Pat. No. 6,040,622, assigned to SanDisk Corporation. Both of these applications and patent are also expressly incorporated herein by this reference.
The newer SD Card is similar to the MMC card, having the same in plan view. A primary difference between them is that the SD Card includes additional data contacts in order to enable faster data transfer between the card and a host. The other contacts of the SD Card are the same as those of the MMC card in order that sockets designed to accept the SD Card will also accept the MMC card. The electrical interface with the SD card is further made to be, for the most part, backward compatible with the MMC product described in version 2.11 of its specification referenced above, in order that few changes to the operation of the host need be made in order to accommodate both types of card. The electrical interface of the SD Card, and its operation, are described in co-pending patent application Ser. No. 09/641,023, filed Aug. 17, 2000, which application is incorporated herein in its entirety by this reference.